The present invention relates in general to data storage systems and, more particularly, to the optimization of system parameter values in a data storage system.
A disk drive is a data storage device that stores data in concentric tracks on a disk shaped medium. Data is read from the medium by spinning the medium about a central axis while positioning a transducer near a target track of the medium to sense the data. The transducer provides an electrical signal representative of the sensed data to data processing circuitry within the disk drive which converts the electrical signal to a format that is recognizable by an attached host unit. The converted data signal is then delivered to the host unit for use thereby. Disk drives can store data in any of a number of different forms, such as magnetic data storage and optical data storage.
To accurately transfer data to/from the target track, the transducer must first be moved from a present location to the vicinity of the target track and then the transducer must be held relatively steady above the target track. Preferably, the transducer element performing the transfer will be substantially centered above the target track during the data transfer. To position the transducer with respect to the track, a servo positioning system is generally implemented. The servo positioning system uses position feedback information read from the surface of the disk by the transducer and a plurality of servo parameter values to perform the desired servo positioning operations. If the servo parameter values used by the servo positioning system are not adequately tuned, the resulting servo positioning operations will be inaccurate and disk drive performance will be compromised.
In the past, servo parameter values were generated by first developing a mathematical model describing the specific servo system being implemented. The mathematical model was then used to determine theoretical ideal settings for the various servo parameters of the system. The theoretical settings would then be applied to the system and the performance measured. If the resulting performance was not as theoretically predicted, as was often the case, further refinement of the mathematical model and/or manual adjustment of system parameters would be undertaken. As can be appreciated, this process of determining an acceptable set of servo parameter values can be complex and time consuming. Manual adjustment of the servo parameter values is difficult because many of the parameter settings in the servo system are dependant on other parameter settings so that adjustment of one parameter value affects the optimal setting for one or more other parameter values. Because of the inherent complexity of the process, the parameter values resulting from such a process are generally far from optimal. In addition, because of variations in physical characteristics between disk drives, optimal servo parameter values for one disk drive are often sub-optimal in other disk drives having the same design.
Therefore, there is a need for a method and apparatus for rapidly, accurately, and efficiently tuning servo parameter values in a disk drive.
The present invention relates to a system that is capable of rapidly tuning servo parameter values in a disk drive. The system makes use of a genetic process for adaptively tuning the parameter values based on simulated evolution. The system requires no complex math calculations and is simple enough to be resident on the drive itself. Because of its speed and simplicity, the system can be used to tune servo parameter values in each individual disk drive in a manufacturing operation. Thus, the system is capable of significantly improving average disk drive servo performance in a high volume manufacturing environment. In addition, the system can be implemented within the disk drive itself, thus allowing periodic parameter re-calibrations to be performed in the field.
In one embodiment of the invention, an initial population of individuals is first generated, each individual including a value for each of a plurality of servo parameters. Fitness values are then calculated for each of the individuals in the initial population. Individuals from the initial population are then chosen for mating based on the calculated fitness values. The chosen individuals are manipulated using genetic operators to produce a new population of individuals. Fitness values are then calculated for the new population and the cycle is repeated. The process is continued until a predetermined criterion has been met. After the process has ended, an individual is chosen based on fitness values and the servo parameters of the disk drive are set accordingly.